1. Field of the Invention
The present invention relates to a resonator having an electrode formed on a dielectric substrate, a filter, an oscillator, a duplexer, and a communication apparatus employing these devices.
2. Description of the Related Art
Resonators formed using a dielectric substrate and designed to exhibit resonance in the frequency band of microwaves or millimeter waves include a resonator realized with a slot line.
In a conventional slot-line resonator, one resonator is realized with a straight half-wave slot line. Such a resonator realized with a slot line is structured to have an electrode continuously formed around a slot line, and can therefore confine electromagnetic energy in the slot line with high efficiency. When the resonator is included as a module in a high-frequency circuit, it hardly interferes with any other circuit. This is advantageous.
FIG. 18A and FIG. 18B show an example of a half-wave slot-line resonator having both ends thereof short-circuited. In FIG. 18A, an electrode 2 having a slot 3 bored as part thereof is formed on the upper side of a dielectric substrate 1. FIG. 18B shows the distribution of the electromagnetic field on the slot-line resonator. In FIG. 18B, solid lines denote the electric field and dashed lines denote the magnetic field.
The efficiency of the resonator realized with a slot line in confining the electromagnetic field depends on the width of the slot. In other words, the larger the width of the slot 3 (slot line), the wider the spread of the electromagnetic field in the slot-line resonator.
The foregoing phenomenon will be interpreted below from a physical viewpoint.
For example, the electric field distribution in a slotted section is as shown in FIG. 19A. When the electric field distribution is expressed as an equivalent circuit, the equivalent circuit is like that shown in FIG. 19B or FIG. 19C. FIG. 19B shows an equivalent circuit for a large-width slot, while FIG. 19C shows an equivalent circuit for a small-width slot. In the equivalent circuit, if the ratio of an electrostatic capacitance C2 (C2xe2x80x2) or C3 (C3xe2x80x2) to the total electrostatic capacitance is large, or in other words, if the electrostatic capacitance C2 (C2xe2x80x2) or C3 (C3xe2x80x2) contributes greatly to the total electrostatic capacitance, the spread of the electromagnetic field is thought to be wide. In contrast, if the ratio is small or if the electrostatic capacitance C2 (C2xe2x80x2) or C3 (C3xe2x80x2) contributes little, the degree of concentration of the electromagnetic field in the slot is thought to be high.
Assuming that the lengths of electric lines of force drawn to pass through points at which the electrostatic capacitances C1 (C1xe2x80x2), C2 (C2xe2x80x2), and C3 (C3xe2x80x2) are detected are w1 (w1xe2x80x2), w2 (w2xe2x80x2), and w3 (w3xe2x80x2), respectively, the electrostatic capacitances are inversely proportional to the lengths of the electric lines of force.
The lengths of the electric lines of force drawn to pass through the points at which the electrostatic capacitances are detected are assumed to change from those shown in FIG. 19B to those shown in FIG. 19C. This signifies that the width of the slot is decreased by a length xcex94w. In this case, the following relationships are obtained:
w1xe2x80x2=w1xe2x88x92xcex94w 
w2xe2x80x2=w2xe2x88x92xcex94w 
xe2x80x83w3xe2x80x2=w3xe2x88x92xcex94w 
In addition, a relationship of w1 less than w2 less than w3 holds. Among the changes from the capacitances C1, C2, and C3 to the capacitances C1xe2x80x2, C2xe2x80x2, and C3xe2x80x2, the change from C1 to C1xe2x80x2 is the largest. Namely, when the width of the slot is small, the electrostatic capacitance C1 (C1xe2x80x2) contributes most greatly to the total electrostatic capacitance. This means that a smaller width of a slot or a slot line leads to a higher degree of concentration of the electromagnetic field.
Therefore, for improving the efficiency of a slot-line resonator in confining the electromagnetic field, the width of a slot or a slot line should be decreased. A high-frequency circuit module is assumed to be composed of a slot-line resonator and another conductive line which are formed using a dielectric substrate. In this case, once the efficiency of the slot-line resonator in confining the electromagnetic field is improved, even if the distance from the slot-line resonator to the conductive line is decreased, undesirable coupling will hardly occur. The high-frequency circuit module can therefore be designed compactly.
When the width of a slot line in a slot-line resonator is decreased, the degree of current concentration at the edges of an electrode increases. Consequently, the edge effect becomes significant and conductor loss increases. The unloaded Q-factor (Qo) exhibited by the resonator decreases. Therefore, if the resonator is employed in a filter or the like, a new problem such as increased insertion loss will occur.
Addressing these problems, the present invention provides a resonator, a filter, an oscillator, a duplexer, and a communication apparatus employing these devices which exhibit improved efficiency in confining an electromagnetic field in an opening of an electrode, suppressed concentration of currents, and minimized conductor loss.
According to an aspect of the present invention, a resonator has a slot-like opening formed in a dielectric substrate. Electrode patterns are formed in the slot-like opening so that the slot-like opening will be divided into smaller-width slot lines. The electrode patterns by which the slot-like opening is divided into the smaller-width slot lines have a width permitting suppression of an edge effect occurring in the electrode patterns.
Owing to the above structure, since the slot lines into which the slot-like opening is divided by the electrode patterns have a small width, the efficiency in confining the electromagnetic field improves. Moreover, the resonator is structured to have a plurality of slot lines, which serve as resonators, juxtaposed and separated by the electrode patterns. The direction of a current flowing along one edge of each of the electrode patterns by which the slot-like opening is divided into the smaller-width slot lines is opposite to the direction of a current flowing along the other parallel edge thereof. The currents flow close to each other in mutually opposite directions. Therefore, loss hardly occurs in each electrode pattern. However, conductor loss occurs at both the edges of each electrode pattern. Assuming that resistors Ra and Rb cause the conductor loss at the edges of each electrode pattern, an unloaded Q-factor Qo exhibited by each slot line is expressed as Qo=xcfx89L/(Ra+Rb). Since the plurality of slot lines is juxtaposed, xcfx89L gets larger in proportion to the number of juxtaposed slot lines. This results in an improved unloaded Q-factor Qo.
Moreover, according to an aspect of the present invention, the electrode patterns are preferably formed only in short-circuited or equivalently short-circuited portions of the slot-like opening so that adjoining slot lines will communicate with a portion of the slot-like opening. Owing to this structure, conduction loss occurring in part of each electrode pattern which exhibits a high current density is minimized effectively. Moreover, the adjoining slot lines into which the slot-like opening is divided communicate with the portion of the slot-like opening devoid of the electrode patterns. Consequently, occurrence of a spurious pulse mode in each of the slot lines into which the slot-like opening is divided by the electrode patterns can be suppressed. Moreover, a portion of the slot-like opening in which the electrode patterns, by which the slot-like opening is divided into the smaller-width slot lines, are formed is so limited that the electrode patterns can be formed easily.
Moreover, according to an aspect of the present invention, the slot-like opening in the resonator is preferably shaped spirally. Consequently, currents flowing along edges formed between two adjoining lines of the slot lines, into which the spiral slot-like opening is divided, are canceled out. Conductor loss occurring at the edges between the slot lines can be minimized more effectively.
Preferably, a plurality of slot-like openings is juxtaposed in the resonator, and the width of each slot-like opening is made larger near an equivalently open position.
Electrode patterns are formed at short-circuited or equivalently short-circuited positions in each slot-like opening so that the slot-like opening will be divided into smaller-width slot lines, whereby the spread of the magnetic field is suppressed. When the slot-like openings are juxtaposed, the degree of coupling among the openings decreases. However, electric fields are dominant near the equivalently open position in each slot-like opening. Therefore, since the plurality of slot-like openings whose widths are each made larger near the equivalently open position is juxtaposed, the degree of coupling between adjoining slot-like openings can be increased.
Moreover, according to an aspect of the present invention, an electrode having an opening as part thereof may be formed on a dielectric substrate, and a plurality of electrode patterns may be extended inwards from the periphery of the opening so that a plurality of slot lines will be arranged substantially radially. The electrode patterns extended inwards have a sufficiently small width. The direction of a current flowing along one edge of each of the plurality of electrode patterns is opposite to the direction of a current flowing along the other edge thereof parallel to the one edge. Therefore, edge effects are canceled out. Moreover, since the slot lines are arranged substantially radially, each of the slot lines adjoins another slot line. The slot lines do not have an edge at which an edge effect occurs. Compared with a resonator realized with a single slot line, the overall conductor loss is suppressed.
According to an aspect of the present invention, a filter includes a resonator having any of the aforesaid structures, and a signal input/output port.
According to an aspect of the present invention, an oscillator is a band reflection type oscillator comprising a reflex amplification circuit and the aforesaid resonator.
According to the above aspect of the present invention, the stability in an oscillation frequency is improved by utilizing the property of a resonator that is a high unloaded Q-factor Qo.
According to an aspect of the present invention, a duplexer is provided with the aforesaid filter as a transmission filter and a reception filter respectively connected between a transmission signal input port and an input/output port used in common for transmission and reception, and between the input/output port used in common for transmission and reception and a reception signal output port.
According to an aspect of the present invention, a communication apparatus is provided with the aforesaid resonator, filter, oscillator, or duplexer.
According to the above aspect of the present invention, a communication apparatus having a small loss and exhibiting high efficiency in utilizing power is provided by making the most of the property of a resonator that is a high unloaded Q-factor Qo. Moreover, since a resonator, a filter, an oscillator, or a duplexer which can highly efficiently confine electromagnetic fields is adopted, these devices and other circuits or devices can be located close to each other. The communication apparatus can therefore be designed compactly.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings, in which like references denote like elements and parts.